Vodacom iPhone water damage excuse to void warranty

I recently (6/8/19) took my iPhone Xs Max 256 gig in to Vodacom Umhlanga Ridge repair centre as my phone had black dots/spots on the screen which seemed to get progressively worse over time since I 1st noticed them a month after receiving the phone brand new in latter 2018 on release day. The reason I did not report or take the phone in earlier is because I did not have a spare handset to replace it as I use my phone extensively for business. We all know trying to get a loan phone from Vodacom is like trying to extract blood from a rock. Anyhow I managed to buy an old iPhone 6 which I’m using whilst my Xs max was sent in. On inspection at Umhlanga Ridge Vodacom I explained the issue with the screen and mentioned there are no other issues with the phone besides the black dots on the screen. The agent was quite positive that they would just swap the handset for another one as they do not repair the Xs max and I thought all well and would collect the replacement the following week. I called the store Tuesday 12th August to inquire as to the progress and to my amazement I was told that the phone is beyond economic repair and that I should come and collect it. I was in utter disbelief and shock; I was told the handset has water damage and that the warranty has been voided and there is nothing I can do. I did not digest this info easily and requested to speak to someone in charge, I was then passed on to a gentleman by the name of Cameron who did another inspection and confirmed that a water indicator was tripped and turned red and he did send a pic of this. I refused to accept this assessment as the iPhone Xs max is IP68 water resistant and in any case my phone did not ever come into contact with water. (Here is a video from the head of marketing of Apple proving that the phone is water resistant, skip to 40m.30s https://www.youtube.com/watchv=wFTmQ27S7OQ&t=2452s ) I made it clear to Cameron that my phone has never come into contact with water, we argued for a bit and said he would put me in contact with a rep from Core but I was not sent this info. My handset was then sent to the advanced repair centre in Johannesburg and here I was told the same story that the phone is water damaged and that I need to pay R15000 for a replacement phone. I asked the agent to prove the link between this water damage that they claim and the black dots on the screen. She said she will escalate the issue and have the technicians contact me. In closing how can a phone that is working 100% only with black spots on the screen be water damaged and what is the correlation between the two? Why advertise it being ip68 water resistant? Out of 20 iphones Xs max opened or assessed, how many have this indicator tripped? Why does Apple advertise the phone being thrown into a pool of water? Why do Vodacom have a warranty in place if it means nothing to the consumer. I’m quite sure we are covered for issues like this under the Consumer protection act. Anybody with a similar experience please feel free to contact me on ***